Messaging systems are known that provide instant, real-time communications between users connected through online or electronic network environments. Examples of online instant messaging (IM) systems include Yahoo!® Messenger and AOL Instant MessengerSM. These systems are becoming increasingly popular among Internet and worldwide web users because they are easy to use and provide a simple way for one user to instantly send a message to another user. However, these systems do not allow users to send voice messages to users on external systems, such as cellular telephone networks.
U.S. Pat. No. 6,430,604 discloses an IM system that is capable of sending messages between users of online and cellular systems. In the '604 system, a separate IM system is provided. The IM system is able to detect which users are logged on. For users not logged on, the IM system provides alternative delivery mechanisms, such as cellular phones, pagers and email. The '604 system transforms its messages for delivery on these external systems when a user is not logged in. Although the '604 system represents an advancement over traditional online IM systems, it does not provide a universal IM service that seamlessly interoperates over different wireless carriers or between cellular handsets and personal computers.
Known IM systems provide real-time awareness of who is logged on to the system. Typically, an IM system user has an address book containing names and/or nicknames for those people with whom he/she communicates. The entries in the address book are used for selecting a message recipient. For a message to be sent instantly from a sender to a recipient, both users must be currently logged onto the IM system. Known IM systems do not store messages for later delivery for each of the intended recipients is not logged onto the IM system.
Some IM systems permit one-to-many message broadcasts. One-to-many broadcasts allow a sender to simultaneously transmit a message to more than one recipient. One-to-many message broadcasting has been used for decades by other types of two-way communication systems, namely, in two-way radio systems, e.g., walkie-talkies, citizen band (CB) radios, and radios used by police and fire departments. In these earlier communication systems, multiple users were required to use the same frequency and would inherently broadcast messages to all of the other users on a channel (one-to many messaging). To facilitate the orderly use of the radio channel, push-to-talk (PTT) communication schemes were devised.
A conventional PTT system has multiple radios, all tuned to the same channel (i.e. the same frequency). Any user who wishes to speak pushes a button on his/her radio, causing his/her radio to transmit to the other radios. Releasing the button causes the sending radio to release the channel for use by the other user. Any number of users may share the same frequency, provided that there is some way to arbitrate the channel usage.
Single channel PTT systems evolved into trunked radio systems. In a trunked radio system, instead of sharing a single physical channel, the users share a common logical channel. A user who wishes to start a conversation broadcasts a signal to a controller requesting such a start. The controller receives this signal and broadcasts back a signal to other users, which allocates a physical channel. The other user radios then automatically re-tune to allocate a frequency and the conversation continues using PTT messages. Whenever there is a pause in the conversation, the controller can allocate a new physical channel. The trunked radio system was an improvement over the single channel system because it could re-allocate physical channels based on traffic patterns, signal quality and the like.
Over the course of decades, PTT messaging has become a customary and familiar way of communication for many people. Consequently, PTT functionality has recently appeared in other types of communication systems. For example, Nextel is currently offering PTT services to its cellular customers. As a further example, U.S. Pat. No. 6,360,093 describes a communication system that permits PTT messaging between digital cellular handsets and networked computers. The '093 system digitizes voice messages and transmits them as streaming voice data messages to users. Although the '093 system and Nextel services present useful applications of PTT messaging, they do not extend PTT functionality into voice/text instant messaging environments. Nor do they address the need to provide seamless PTT functionality and instant messaging between users on different wireless carrier networks.
Accordingly, there is a need for an improved communication system that allows seamless instant messaging with PTT functionality.